Kirkland Omega-3 capsule has fishy taste

No, that's absolutely not true. There is a lot of bullshit online. It's made from fish. Of course it will taste like fish. Being rancid means something completely different, and you would really know if it was. That's not a fishy smell. It's a disgusting smell. The only way to empirically measure the quality of fish oil in regard to rancidity is through a peroxide test. Our limits on our fish oils are 5 mEq/Kg or less. Rancidity starts happening in the 30-40 mEq/Kg range. Also, some fish taste more or less fishy. So the species of fish you use in the oil affects its smell and taste. One fish oil with a 2 mEq/Kg peroxide value could taste totally different than another oil made from a different species, even if that one also has 2 mEq/Kg. There is a lot more to fish oil taste than its oxidation levels. The only way for you to really know the oxidation levels of the fish oil you bought is to ask them for a COA with the peroxide levels on it. You can also deodorize fish oil in a special process. So you can mask the oxidation levels by deodorizing it. The only real way to know is to test it. I have no idea if Kirkland is having their contract manufacturer test every finished batch of fish oil softgels for peroxide levels. Kirkland is just a brand that has contract manufacturers white label products for them. The quality of the products will depends on the specific contract manufacturer they use for that product.